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ESD procedures


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#1
fay47

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Can someone please explain the correct ESD procedures to use when working on the inside of a computer using a wrist strap. I have read that when using a wrist strap the computer should itself be grounded. I have also read that the best way to ground the comptuer is by having it plugged into a grounded outlet. But I also thought that the computer should be unplugged before working on it.

So what is the correct procedure.


Thanks, Fay
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#2
Kemasa

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Ok, you want the correct procedure, so here it is.

The machine should be unplugged (otherwise there is still power there). You should use a static mat and place the computer on the mat. The mat needs to be grounded. The wrist strap should attach to the mat and the resistor should be check from time to time to ensure that you don't have a problem with it.

Also, you should no wear clothes which can generate static electricity, so short sleeves are typically best.

You can also go on from there and ensure that the chair you use is grounded and that the floor is acceptable, but it all depends on how far you want to go.

So, that is the correct procedure, but often people don't follow those procedures (myself included). While it is important to realize that some damage can occur and that it could cause a failure over time, sometimes it is worth it to take the risk (assuming that it is your machine). If you turn off the power, including the switch at the back of the machine, touch bare metal of the machine and set the parts in the envelope on the bare metal, you can typically get away with it. If there is no power switch at the back, I would not leave it plugged in since there is still power in the machine.

BTW, when you get gas, you should always touch the metal of the side of the pump before touching the nozzle or anything near where gas vapors might me. This includes groundiing yourself if you sit in the car while waiting for the gas to fill. Most people don't do this and get away with it, but some don't get away with it (who cares if it is one in a miillion if you are the one).
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#3
fay47

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Hmmmmm, ok. Guess I'll have to watch the way I word my questions :tazz:

I don't have a static mat and at this point do not plan to buy one. I do have a wrist strap. I read your reply and am still not really sure about the correct use of the wrist strap - when using only the wrist strap and nothing else.

What I really wanted to know was just this. If I wear the wrist strap and attach it to the computer case, plugged in or unplugged? Does the wrist strap do any good if the computer is unplugged which I guess would leave the computer un-groudned? This may be a dumb question to some but I don't know the answer so I ask it anyway.

Fay
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#4
Kemasa

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What are you planning on doing on the machine? This makes a bit of difference, but remember this is not the recommended procedure, so you takes your chances :-).

If I were to work on the machine, I would turn the back switch off, which cuts all power to the machine. Then attach the wrist strap to bare metal of the case. Take what I am adding to the machine and set it on the bare metal, then open the envelope and install it. All the while trying not to move around too much. I have also disconnect the power and just used the case keeping everything at the same potential static-wise. Not the best thing to do, but I am willing to take the risk and I have a complete static kit, so perhaps I should not answer the question :-).

If there is not a power switch, then I would unplug it. If I was working with anything related to the power supply, excluding power connections to devices like disks, I would unplug it.

It is not a dumb question. In part I think it is good to know the right way and then decide how much risk you want to take. If you are careful, then I don't think there is much risk. I will say that being careless with a complete static kit can be worse than being careful with nothing.
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#5
fay47

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Thanks for the reply. I don't have anythng planned right at this time. I have just been confused by what I have read and heard on ESD procedures.

Have read that you should use a wrist strap attached to a properly gounded case, but the article did not tell what it considered a properly grounded case. In completly separate article, read that the best way to ground a computer was thru a grounded plug-in. In still a different article, I read that the computer should be un-plugged before working on it. I tried looking at different sources but basically found the same thing - no article I found - told the complete answer.

Had one person tell me to open the case, touch a metal part of the case with both hands, then attach the wrist strap and then unplug the computer and leave the writst strap on. Does the wrist strap do any good at that point with the computer unplugged?

To me, the information is confusing and contradictory. When using a wrist strap - to leave plugged in or to un-plug - that is the question. :tazz:

Thanks for your input.

Fay
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#6
warriorscot

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You get a static discharge when there is a difference in the charge between yourself and the computer, by using the wrist strap you remove the difference so both can be loaded with static and so can the case but as long as you and the case have an equal charge there can be no discharge.

Edited by warriorscot, 30 December 2005 - 07:37 PM.

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#7
fay47

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OK, then you are saying that having the wrist strap attached works even with the computer un-plugged - is that correct?

Fay
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#8
Kemasa

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A properly grounded case is one in which the frame of the machine is attached to a good ground, typically using the ground in a power plug, but only the ground and not the power.

You should not really have the machine plugged in since that means there is power and where there is power, there can be a nasty shock, although not static, but it could kill or injure you. For the most part you are protected because the AC power in enclosed in the power supply, but there can be power, low voltage DC, being supplied even when the machine is "off", which is why you need to turn the power switch off at the back of the machine.

Yes, you can touch the bare metal of the case (best to always keep one hand on the bare metal, but as long as you don't general any static electricity then it is ok, but that is hard to know).

Yes, the wrist strap will still be good since it will keep you and the machine at the same potential with respect to static electricity. It is not quite the same as having everything grounded, but it is typically good enough, especially if you are careful.
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#9
fay47

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You said:
"A properly grounded case is one in which the frame of the machine is attached to a good ground, typically using the ground in a power plug, but only the ground and not the power."

But then I don't know of a way to do that, and by what you said below that, I gather maybe there is not a way - unless you mean by turning off the power switch on the computer. I do not have a power switch on the back - thought I did - but checked and I don't.

So, then I gather that I shouuld use the wrist wrap with the computer unplugged.

Thanks again,
Fay
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#10
Kemasa

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The way to ground the machine like that is with a static kit. You could also take a power cord and remove the two wires for the power.

Yes, with no power switch on the back, then use the wrist strap with the computer unplugged. As I said, take any items you are installing and place them on the bare metal of the case, if possible. While it is not the proper way, it will typically work without a problem and it gets the job done.
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#11
fay47

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OK, thanks for you patience.

Fay
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